In the art of manufacturing tires, it is desirable to employ rubber vulcanizates that demonstrate reduced hysteresis, i.e., less loss of mechanical energy to heat. For example, rubber vulcanizates that show reduced hysteresis are advantageously employed in tire components, such as sidewalls and treads, to yield tires having desirably low rolling resistance. The hysteresis of a rubber vulcanizate is often attributed to the free polymer chain ends within the crosslinked rubber network, as well as the dissociation of filler agglomerates. Functionalized polymers have been employed to reduce hysteresis of rubber vulcanizates. The functional group of the functionalized polymer may reduce the number of free polymer chain ends via interaction with filler particles. Also, the functional group may reduce filler agglomeration. Nevertheless, whether a particular functional group imparted to a polymer can reduce hysteresis is often unpredictable.
End-functionalized polymers may be prepared by reacting a functionalizing agent with an active polymer chain (e.g., a living polymer chain). For example, anionic initiators are known to be useful for the polymerization of conjugated diene monomers to form polydienes having a combination of 1,2-, cis-1,4- and trans-1,4-linkages. Anionic initiators are also useful for the copolymerization of conjugated diene monomers with vinyl-substituted aromatic compounds. The polymers prepared with anionic initiators may have an active end, which may also be referred to as a reactive chain end, that may be capable of reacting with additional monomers for further chain growth or reacting with certain functionalizing agents to give functionalized polymers.
But, the ability to react functionalizing agents with active polymer chains can be unpredictable. Moreover, the ability to choose functionalizing agents that will yield a desired degree of hysteretic loss within particular vulcanizates is unpredictable.
Because functionalized polymers are advantageous, especially in the manufacture of tires, there exists a need to develop new functionalized polymers that provide vulcanizates with reduced hysteresis.